Hi,

I went to look at an '88 van with a 351w, we did a compression test and got:

1 - 180
2 - 185
3 - 190
4 - 170
5 - 168
6 - 170
7 - 170
8 - 173

We think this is pretty good, number 3 seems a little high compared to the others (carbon build up?). The engine ran fine, with no knocking or odd noises. The plan is to swap this engine into my '91 F250 4x4 (manual trans), which currently has a 5.0. I am not going to rebuild it.

Anyway just wondering what others have got for results for their compression tests.

And does anyone have a link to the specs for this engine? hp, tq, compression etc...

Thanks.

 

Normally you won't or at least I haven't found a set compression figure usually they say they should all be within 75% of the highest number. If you saw the compression numbers I posted earlier for my 87 then you must realize that the numbers you have are great if the engine has decent miles on it. As far as hp and torque it falls somewhere around 210hp and 295 torque. Good luck

 

Hi,

Thanks. We even double checked a few cylinders with a second gauge and the numbers were the same. Don't really understood why the compression numbers are not published... oh well. I was going to do a full rebuild on the engine but I think I may just swap it in and save some money.

Greg

 

They should be 15%. If you use the 75% rule you could have a cylinder at 25psi and the highest at 100psi.

 

Your close, actually how you figure the 75% of the highest rule of thumb is you take the highest number you have then take it times .75 which would give you if your highest number was 100 a lowest psi of 75 not 25.


His highest being 190 and the lowest being 168 means that the lowest should not fall below 142.3 and the 168 is well above.

Hopefully the bearings are in as good a shape and the old motor will give you some dependable service, good luck

 

 

Don't forget to check the valve lash before testing the comp. as a titer lashed valve will open sooner and close later thus letting more of the incoming charges at slow speeds out the exhuast.

Worn camshaft will mess with cranking compresion numbers to.

Best of luck

44Dwarf

 

I ressurected this thread to ask a few compression test questions...
...I was looking at Greg's compression test results as I have a 351w in an 87 f250 2wd with a c6 tranny. The results I got are much lower readings around 125-130 for each cylinder. The truck has had a few power problems come up recently. I'm planning on an engine rebuild in the spring but was wondering how far I would have to go into the engine or do I just need to go ahead do a complete rebuild on everything? Although I've rebuilt engine's before just checking my basis.

When I rebuild the engine I'm going to attempt my very 1st tranny rebuild by myself, Wish me Luck!

Any and all comments are welcome and appreciated!
Thanks!...---Rob---